1. Field of the Invention
This invention relates generally to thermoplastic elastomer (TPE) materials. Thermoplastic elastomers are broadly defined as rubber-like materials that, unlike vulcanized rubbers, can be processed and recycled like thermoplastic materials, yet have properties and performance similar to that of vulcanized rubber at service temperatures. A particularly useful subset of thermoplastic elastomers is those prepared as dynamically vulcanized alloys, or thermoplastic dynamic vulcanizates (“TPV” compositions). The invention more specifically relates to thermoplastic elastomer TPV compositions that have been modified for improved adhesion to polymeric substrates, and particularly with respect to polar engineering thermoplastics.
2. Description of the Prior Art
Polymer blends which have a combination of both thermoplastic and elastic properties can be obtained by combining a thermoplastic resin with an elastomeric material in a way such that the elastomer is intimately and uniformly dispersed as a cross-linked, discrete particulate phase within a continuous phase of the thermoplastic. Early work with the vulcanization of the elastomer phase is found in U.S. Pat. No. 3,037,954 which discloses static vulcanization, as well as dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured (crosslinked) while continuously mixing and shearing the blend. U.S. Pat. No. 4,130,535 discloses thermoplastic elastomer compositions comprising thermoplastic olefin resins and olefin copolymer rubbers, prepared by dynamic vulcanization and wherein the rubber component is vulcanized to the extent that it is essentially insoluble in conventional rubber solvents.
The thermoplastic phase of TPV compositions can be principally composed of any of a number of other thermoplastics, not just the thermoplastic olefins mentioned above. U.S. Pat. No. 6,207,752 describes TPV compositions comprising carboxylated-nitrile rubber and thermoplastic polyurethane to achieve low oil absorbance, non-stickiness, and ready processing characteristics. U.S. Pat. No. 6,291,587 describes thermoplastic vulcanizates comprising a thermoplastic polyurethane not having a major glass transition temperature less than 60° C., and a cross-linked, non-polar rubber, such as an ethylene-propylene-diene rubber. It further suggests generally that properties can be improved by the addition of compatibilizers. International Pat. Applic. No. WO 01 10950 (A1) describes thermoplastic vulcanizates comprising a thermoplastic polyurethane having a major glass transition temperature less than 60° C., and a cross-linked, non-polar rubber, such as an ethylene-propylene-diene rubber. It further suggests generally that properties can be improved by the addition of compatibilizers.
Specific efforts to improve the adhesive properties of thermoplastic elastomers have been made through the incorporation of functionalized thermoplastic resins into the blends. One approach is described in U.S. Pat. No. 4,957,968. The description discloses the addition of a functionalized polyolefin to improve adhesion to metals and polar polymers. Further, U.S. Pat. No. 6,503,984 describes a combination of a low flexural modulus and low crystallinity polyolefin and a functionalized polyolefin that was found to result in an olefin composition with excellent adhesion to metals and polar polymers (e.g. polyesters, polyamides, etc) especially fibers therefrom. U.S. Pat. No. 5,852,118 addresses block copolymers of polyolefins with polyurethanes, copolyesters, or copolyamides for improving adhesion of a typical polyolefin based TPV to polar engineering thermoplastics. U.S. Patent Applic. No. 2003/0083434 A1 describes adhesive compositions containing 25 to 95 wt. % thermoplastic elastomer and from 10 to 75 wt. % of a specific block copolymer, wherein the thermoplastic elastomer contains a polyolefin thermoplastic and a cross-linked olefinic rubber, optionally with 10 to 50 wt. % thermoplastic polyurethane.
Despite these solutions for adhering TPV compositions to polymer substrates, and particularly to polar engineering thermoplastic substrates, further improvements in bonding strength with compositions having excellent TPV engineering properties are still being sought.